Automatic screw-cutting lathe



April 17, 1951 BQDMER 2,548,937

AUTOMATIC SCREW CUTTING LATHE Filed April 8, 1946 Patented Apr. 17, 1951 AUTOMATIC SCREW-CUTTING LATHE Ernest Bodmer, Grand-Lancy-Geneva, Switzerland, assignor to Tarex S. A., Geneva, Switzerland, a corporation ofSwitzerland Application April 8, 1946, Serial No. 660,503 In Switzerland June 6, 1945 2 Claims. 1

Automatic screw cutting lathes most appreciated at the present time are provided with a device for controlling the movement of the crossed slides of the tool holder having a lead screw, driven in rotation, cooperating with a nut sliding parallel to the axis of the lead screw and capable of oscillating in a. plane perpendicular to this axis. Cams produce at the beginning and end of the working stroke the engagement and disengagement respectively of the nut with the lead screw. The movements of the nut, parallel to the axis of the lead screw, control the movements of the longitudinal slide of the tool holder. These lathes have certain disadvantages due to the fact that the nut must be capable of carrying out movements in two planes perpendicular to one another on the one hand, and on the other hand due to the fact that the disengagement of the nut from the lead screw at the end of the working stroke is produced by a cam. In fact in order to enable the nut to carry out movements in two planes perpendicular to one another, manufac-v turers have in general secured the nut toa sleeve mounted on a rod capable of sliding in its bearings. It'will be obvious that such a mounting is difficult to realise as when a great precision of screw cutting is required, the clearances must be reduced to a minimum. Further the sleeve has in general a collar adjustable in longitudinal position. The collar is provided with a nose adapted to cooperate with the cams at the beginning and end of the working stroke of the tool. But it is clear that the bearing length which the said nose can present to the cam which acts thereon is at the maximum equal to the pitch of the thread of the lead screw. The nose and the cam thus wear rapidly and the control of the release of the nut is liable to be effected a revolution too late. Consequently the tool is liable to bite into the material and either be broken or in any case heated to such a temperature that its resharpening is necessary. But after each resharpening the whole adjustment of the lathe must be effected afresh and controlled if it is desired to obtain a precision screw thread. Further according to the degree of wear of the nose cooperating with the cam, it is possible that the nut remains half engaged with the lead screw. In this case there occurs a local rapid wear of the lead screw and nut.

From the foregoing it will be seen that the lead screws and the nut of known automatic screw lathes wear relatively rapidly and particularly nonuniformly so that it is necessary to test them frequently.

For the purpose of eliminating some of the disadvantages referred to, some manufacturers have hinged the nut holder directly on the longitudinal slide of the tool holder carriage. Such a construction, however, is not desirable as it increases the weight of the. tool holder carriage of the lathe. But in view of the high cutting speeds possible at the present time by reason of the special steels placed on the market, the return of the slide to the starting position should be more rapid as it should be effected in a period of time considerably shorter than the duration of a complete revolution of the cam shaft controlling the engaging and disengaging movements of the nut, and that this cam shaft cannot be driven at a speed much "less than that of the lead screw, or else the engagement and disengagement ofv the nut is not efi'ected in a precise manner.

The present invention has for its subject a device for controlling the movements of the longitudinal slide of the tool holder of a screw cutting lathe, which tends to eliminate the disadvantages referred to. This device is provided with a lead screw cooperating with a nut and is distinguished from known devices by the fact that the lead screw is movable axially and is connected by connecting members to the longitudinal slide of the tool holder and by the fact that the nut, movable in a plane perpendicular to the axis of rotation of the lead screw, is held against any movement parallel to the said axis.

One form of construction of the subject of the invention is shown diagrammatically and by way of example in the accompanying drawing.

In the drawing only the members necessary for the understanding of the devices for controlling the longitudinal slide have been shown.

The spindle I of the screw cutting lathe, pivoted in bearings 2, is driven by a motor M. The part 4 to be screw threaded is held clamped in the spindle by one of its ends Whilst its other end is held in position by a back centre 5.

The lathe is provided with a tool holder carriage with crossed slides, of which the transverse slide 5 is guided by guides provided in the framework 3 and carries the longitudinal slide 1 guided by guides, provided in the transverse slide 6. The longitudinal slide 1 is subjected to the action of a return spring 8 tending to hold it in engagement with a rest stop 9 adjustable in position.

The longitudinal slide 7 is connected by transmission members to a lead screw or master Ill. The latter is driven in rotation by the motor M and by means of an interchangeable gear train. The lead screw is mounted rigidly on a shaft ll of which one end 12 is grooved and slides inside a sleeve l3. This sleeve rotates in a bearing l4 provided in the framework of the lathe and carries two gears I5, l6 each secured rigidly to one of its ends. The gear l5 gears with a toothed wheel ll secured to the shaft of the spindle I. The shaft H is thus driven in rotation by the motor M, further it is connected by means of a coupling l8 to a pusher l9 sliding in a guide 2. provided in the framework of the lathe. A finger 2i, engaging with a groove 22, prevents any angular movement of the pusher. At its free end the pusher carries a finger 23 engaging with a transverse groove 24 of the slide 1. The nut 2-5 slides in a seating 26 provided in the framework. An actuating finger 2! engaging with a seating 28 controls the movements of the nut producing its engagement with and its disengagement from the lead screw 10. The finger 2! is mounted rigidly on a shaft 29 turning in bearings provided in the framework of the lathe. The shaft 28 also carries 'a lever '39 of which the free end cooperates with a cam 31 producing the engaging movements of the nut at each return of the carriage to the normal position. The cam 31 is secured to a shaft 32 driven in rotation by the motor M and by means of gears ll, [*5, I6, 33, 34 and "a clutch 35. The disengagement of the nut, on the contrary, is produced by a quick action relay set in operation at the end of each working stroke of the tool. This relay is formed by a spring mounted on a rod Iill sliding in seatings provided in the framework and carrying a rack in and a pusher 10'3.

The rack I02 engages with a toothed sector "4 mounted rigidlyon a shaft I and provided with an arm [06 of which the end cooperates with a finger lfil. The latter is mounted on a shaft I08 of which the angular movements are controlled, against the action of a return spring I09, by the movements of the longitudinal slide 1.

A second toothed sector lHl, secured to the shaft hi5, engages with a toothed sector ll! secured to the shaft 29 and thus connects the rod l0! mechanically to the finger 21 which controls the movements of the nut.

The pusher H33 isconnected by a train of transmission members:

1. To a crank pin 60 for controlling the advance of the tool in depth between each cut,

2. To an oscillating finger 6| engaging with a groove 62 of the rule 4! and controlling the movements of this and thus the withdrawal and engagement of the tool with the workpiece which is being machined at the end and beginning of each cut.

The engaging and disengaging movements of the driving'and driven parts of the clutch 35 are controlled manually. For this purpose one of the parts of the clutch 35 is connected by means of transmission members to an operating member L. The latter is also connected, by a train of transmission members comprising a shaft H2 rigid with handle L and gear I I3 meshing with gear l'll'on shaft 115, to a sleeve 36 fixed to shaft [l5 carrying a toothed sector 3T engaging with a rack (ta-sliding in a guide 39 provided in the transverse slide 6. The end 40 of this rack cooperates with the -lateral face of a rule 4| sliding in a guide 42 of the slide 6. The guide 42 is arranged in a plane perpendicular to the plane of the guide 39 anda spring 43 tends to hold the lateral face of the rule in contact with the end 40 of the rack.

, The operation of the member L thus produces simultaneously:

1. The engagement of the driven and driving parts of the clutch 35,

2, Thesetting in the transverse position at the start of operation of the tool holder carriage by the movement of the transverse slide 6 against the action of its return spring 43 which tends to hold it in the position of rest, that is to say in engagement with a rest stop &4 adjustable in position.

The angular movements of the sector 31 pro ducing the feed in depth of the tool between each cut are controlled by a device described in a co-pending application of the same date.

The operation of the device for controlling the movements of the longitudinal slide is as follows:

The motor M being under voltage, the setting in operation of the device is obtained by the operation of the manual member L, in a clockwise direction, so as to bring it up to the position shown in the drawing. This operation produces the engagement of the driving and driven parts of the clutch 35 on'the one hand, and on-the other hand the actuation-of the transverse slide 6 from its position of rest, against the action-of its return spring, up to the advanced position (position shown) in which the tool is not yet in engagement with the part 4.

When the clutch 35 is in the engaged position the shaft 32 sets in rotation the cam 3| which produces an angular movement of the arm the end of whichrests on its profile. This angular movement of the arm '36 produces:

1. The swinging of the finger 21 and the engagement of the nut 25 with the threads of the lead screw l0,

2. By means of the toothed sectors IH, H0, I04 and therack I62, themovement, towards the right of th drawing, of the rod NH and the compression of the'spring Hill.

3. The angular movement of the arm H16 up to the position shown'in the drawing, for which the finger lil'l, cooperating with the end of the said arm prevents any movement of the rod Ill! under'the action of the spring I08,

4. By means of the pusher N3, the movement of the rule towards the leftof the drawing and the transverse feed of the slide 6 bringing the point of the 'toolfiush with the surface of the part to be machined,

5. By means of the pusher Hi3, the'rotation in a clockwise direction, of the actuating crank pin for the feed in depth. 'This angular movement of the crank pin Ell produces by means described in the copendingapplication the feed in depth of the tool.

As the lead screw is rotating and the nut engaged, this issubjected to an axial movement towards the right of the drawing. During its movement it so drives the slide 1 that as the part 4 is being driven in rotation by the motor M, the tool 19 cuts-a thread.

At the end of the working stroke, a stop 8| actuates a pusher 82 against the action of the spring H89 and produces the disengagement of the 'bolt I01, I06 which holds the relay in the set position (position shown).

From now on the relay, formed by the spring I08, is set in action andproduces:

l. The-suddenand rapid return-of the nut,

2. The movement to the right of the drawing of the rule 4| and the recoil of the slide fias also the disengagement of the tool from the part which is being machined.

As the nut is "disengaged from the lead screw, the spring 8 repels the longitudinal slide 7 up to itsQposition of rest, defined by the stop 9.

As the shaft 32 continues its rotatio'nthe cam 3| again actuates the lever 30 and the same cycle of movement is effected a second time.

However in order to prevent the cam 31 from actuating the lever 39 at the moment of opening the bolt I01, [06 which would prevent thewithdrawal of the nut, an interlocking device is provided. This device prevents the action of the lever 30 by the cam 31 as long as the bolt I96, In? is in the position shown in the drawing, that is to say in the closed position. This device is formed by a bolt 83, 84 held in the closed position (position shown) by a spring (not shown). The part 83 of the bolt, carried by the lever 98 and pivoted at 85, is actuated, against the action of the return spring, at the end of the return stroke of the longitudinal slide. For this purpose the pusher l9 carries a driving finger 85 adapted to cooperate with a pin 81 secured to the lever 88. The cam 3! slides on the shaft 32 and a spring 89 tends to hold it out of range of the lever 30 so that it cannot produce the oscillation of said lever. The second part 39 of the bolt is form-ed by an arm secured to a sleeve 99 mounted loosely on the shaft 29. This sleeve carries a second arm 9| carrying a pin 92 adapted to cooperate with a ramp 93 secured to the cam 3 I.

When the bolt 83, 84 is open, the arm 9i oscillates and the pin 92 cooperating with the ramp 93 moves the cam 35, against the action of its spring 89, through an amount suflicient to cause it to cooperate with the lever 30. Thus it is only When the longitudinal slide is in the position of starting the machining that the cam 3| can pro duce:

1. The engagement of the nut with the lead screw,

2. The resetting of the relay formed by the spring [00,

3. The feed in depth of the tool,

4. The setting in the operative position of the tool by actuating the rule 4 l.

Thus the security in operation is complete and no error of control can be produced irrespective same movements as the lead screw, which ensures the precision of the pitch of. the screw thread on the part 4, clearances being capable of being reduced easily to a minimum and on the other hand as the thrusts always act in the same direction, these clearances are practically eliminated. Further the disengagement of the nut is controlled by a quick action relay set in operation by the movements of the longitudinal slide in such a manner that this disengagement is always controlled with precision at desired moments on the one hand, and is effectuated on the other hand by a sudden and rapid movement of the nut under the action of the relay, whereby there is avoided as far as possible wear of the nut and local wear of the lead screw.

Further the entire device for controlling the movements of the crossed slides of the tool holder carriage may be secured on the framework of the lathe in such a manner that the carriage is relieved of the whole of the weight of these latter. This results in greater stability of this movable part and thus in greater precision in machining. The inertia of the parts in movement being less, the wear of the lathe is reduced correspondingly.

A form of construction of the device for controlling the movements of the longitudinal slide of a tool holder of a screw cutting lathe has been described with reference to the accompanying drawing. However it is clear that this device may be applied to the control of the longitudinal slide of tool holders of different conception for example with a lower longitudinal slide and an upper transverse slide.

Further the control of the disengagement of the nut may also be effected, in the same way as in known devices, by a second cam mounted on the shaft 32. Finally the nut may be pivoted atits free end on a shaft parallel to the axis of the lead screw. Angular movementsin a plane perpendicular to the axis of the lead screw-may then be controlled directly by cams mounted on the shaft 3-2.

I claim:

1. In a screw cuttinglathe, the combination, comprising, a frame, a slide mounted for movement longitudinally of the frame, a lead screw connected to the slide and mounted in said frame for rotation and axial movement, a motor rotating said screw, a lead nut held by saidframe against movement parallel to said screw and engageable with same to move same axially during rotation, spring means for holding said nut out of engagement with said screw, means holding said nut in engagement with said screw against the action of said spring means, and a locking device preventing stressing of said spring means and the engagement of said nut with said screw as long as said longitudinal slide is out of its position at the starting end of the work stroke.

movement longitudinally of the frame, a lead screw connected to said slide and mounted in said frame for rotation and axial movement, amotor rotating said screw, a lead nut held by said frame against movement parallel to said screw and engageable with same to move same axially during rotation, spring urged means normally holding 7 said nut from engagement with the screw, means operable by the motor and holding said nut in engagement with said screw and connected to said spring urged means and during its operation stressing the spring thereof, and a locking device preventing the operation of the spring stressing means and the engagement of said nut with said screw as long as said longitudinal slide is out of its position at the starting of the work stroke, said locking device being releasable by the lead screw and rendering the nut holding means inoperative.

ERNEST BODMER.

REFERENCES CITED- The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 400,550 Darling Apr. 2,11889 1,125,905 Hazelton Jan. 19, 1915 1,520,494 Drake Dec. 23, 1924 2,101,754 Randall Dec. '7, 1937 2,286,715 Cheever June 16, 1942 FOREIGN PATENTS Number Country Date 88,416 Germany Aug. 25, 1896 14,424 Great Britain July 30, 1903 of 1903 519,560 France Jan. 26, 1921 

